Q.
I have a friend that has got me thinking about
mayflies...and I am stumped. He says that he
witnessed a hatch of some small insects that
appeared to be almost like a blue wing olive
one day. Quite a few got trapped in his vehicle
since he left his windows open. We he got up
the next morning, and as the temperature started
rising, he noticed that the small flies were
hatching or shedding again! Only this time,
the flies were much more pale in color and
slightly smaller. Anyway, I just wanted to
know if this is a normal occurrence with some
mayfly species, or if we are just imagining it!

A.
No, you didn't imagine anything. What you
witnessed was quite common in mayflies.
These insects initially hatch from the nymph
into a sub-adult, or imago, form which is duller
in color and less active and which anglers refer
to as the "dun." After a short period of time,
they undergo a second molt into the true
adult - usually, as you observed, lighter in
color, shiny, and active. It is in this form
that they take flight and mate.

The 'Stream Doctor' is a retired professional stream ecologist and
author, now living in the West and spending way too much time
fly-fishing. You are invited to submit questions relating to
anything stream related directly to him for use in this Q & A Feature
at streamdoctor@aol.com.

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